Electrical musical instrument



Aug. 19, 1952 L. E. A. BoURN ELECTRICAL. MUSICAL INSTRUMENT Filed Aug. '7, 194'? Patented Aug. 19, 1952 UNITED STATES PATENT OFFICE A 2,607,255 i f i ELECTRICAL MUSICAL INSTRUMENT Y` Leslie Edwin Alexander Boum, Ashford, England Application August 7, 1947, Serial No. 767,204 In Great Britain February 7, 1945 Section 1, Public Law 690, August 8, 1946 Patent expires February 7, 1965` This invention relates to electrical musical instruments of the kind comprising a multiplicity of tone generators, and means whereby said generators can be made to speak selectively under Control of keys and stops. The invention is applicable toy any arrangements in which the generator outputs are potential and/or current controlled.

The object of the invention is the provision of a new andimproved way of eiecting the control of the generators by the keys and stops.

The invention consists broadly in the provision of bus bars whose potentials are controlled -by the stops, and potentiometer resistances adapted to be connected across said-bus bars in response to the actuation of the keys, said potentiometer resistances `having tapping points adapted, according to their potentials to control the speech of the tone generators, so that, upon actuation of a key, the tone generators appertaining to said key will speak at a loudness depending on the potentials of said bus bars.

In order that the invention may be the more clearly understood certain embodiments thereof will now be described rreference being made to the accompanying drawings, wherein:

Figure 1 is a circuit diagram illustrating the controlling function of the keys.

Figure 2 is a circuit diagram illustrating a variation of the arrangement shown in Figure 1.

Referring first to Figure 1, each key (not shown) when actuated brings, by connecting means I6, two key contacts I and 2 into engagement with respective bus bars 3 and 4 which are common to all the key contacts, and each pair of key contacts has a potentiometer resistance connected between them. The bus bars 3 and 4 are connected to variable voltage tapping points on a source of supply (not shown.) and their potentials can therefore be varied, This variation is effected by means of stops or other means (not shown). Along the length of the potentiometer resistance 5 tap-ping points 6 are taken through rectiers I5 to terminals I'I which in turn are taken to the control circuits which control the outputs from the individual generators appertaining to that key, say the harmonics of the note represented by said key. Said tapping points G, in the order from one end of the potentiometer resistance 5 to the other, may be taken to the control circuits of the lirst, second, third, fourth, fifth, etc. harmonics of the said note. Each pair of contacts I, 2, together with its associated components 5, 6, I5 and I'I are comprised in a key-circuit unit designated by the reference A.

5 Claims. (C1. S11-1.19)

In the arrangement illustrated in Figure 1 the generator outputs are shown as being controlled by the general method described in my co-pending application Serial No. 767,2D3, filed August 7, 1947, which issued as Patent No. 2,579,358, December 18, 1951, with reference to Figure 1 oi said co-pending specification. Thus the reierence 1 designates one of the generator structures and. the reference 8 the individual generator elements thereof. Each of these generator elements is connected to a terminal I8 and thence by way of' a terminal I9 to the control grid of a pentode valve 9 which is individual to said generator element, and whose output supn plies through terminals I0 the terminals 2D of the common loud speaker or speakers. Each generator structure "I, together with its terminals I3 and a terminal 2I which is connected to the common scanning element of said structure, is comprised in a generator unit designated by the reference B. A resistance Il is connected in the cathode circuit as in said co-pending specication aforesaid, and a source or potential I2 is provided which normally keeps the control grid at a negative potential equal to, or just in excess of, the cut-ofi" value, said source I2 communicating with said grid by rway of 'resistances 'I3 and I4 in series, resistance I4 being of high value, say one to iive megohms, and resistance I3 being normally of the order of 1000 ohms. Thus, resistance II is connected between the cathode of the valve Sand a terminal 22, and the control grid is connected, through said resistances I4 and I3 in series, to 'a terminal 2.3, and said terminals 22 and 23 are respectively conu nected to the terminals 24 and 25 of said source I2. Other details of the circuit will be understood by reference to said co-pending application Serial No. 767,203, led August 7, 1947.

The appropriate tapping point 6 is connected, through the rectifier I5 and terminal I'I to a terminal 26 which is connected to the junction point between the resistance I3 and I4. Each valve 9, together with the associated resistances II, I3, I4 and the terminals Il?, I9, 22, 23, 2S is comprised in a control unit designated by the reference C. The individual generator elements 8 are continuously generating but owing to the negative grid bias of the valve no output normally reaches the loud speakers, and the instrument is normally silent. If the bus bars 3 and 4 are at valve-cut-off potential relative to the cathodes of the valves 9, the note will remain silent on allharmonics when the key is actuated. If the bus bars Sand 4 are raised to the maximum potential above cut off, the appropriate valves 9 will be given their maximum amplication when the key is actuated and all the harmonics will sound at full strength. If the bus bar, say 3, at the low-harmonic end is at maximum voltage and that, say 4, at the high-harmonic end is at cut off voltage, then the irst harmonic will sound at substantially maximum strength and the succeeding harmonics at progressively diminishing strength. The more negative the bus bar 4 at the high-harmonic end becomes the greater the rate at which the upper harmonics will be cut off. The opposite eiect will of course be obtained when the bus bar at the high-harmonic end is at maximum potential and that at the low-harmonic end is ata potential below cut-off.

The voltage applied to the bus-bars@ and 4 may be controlled by stop contacts either b-y the shunt path method as described in British Patent No. 622,910, or by the below cut-off method as described in British Patent No. 613,812.

It will be seen that the resistance I4 serves only to convey the potential to the grid and toprevent the audio signal from being shunted appreciably. Where borrowing is adopted different tappingpoint circuits of diierent potentiometersmay be connected to the same valve 9, and the resistance i3 yforms a common load resistance for all such circuits. The rectiers l5 prevent interaction between energisedand idle circuits.

The spacing of the tappings on the potentiometer may be equal, but in some cases unequal spacing may be employed.

As musical tones mostly divide into `two main classes, viz., those containing only odd harmonics and those containing a complete series, it is convenient to employ, for each key, yone potentiometer the tappings on which are connected to the control valves of only the odd harmonic series of generators for that note, and a second potentiometer the tap-pings on which are connected to the control valves of only the leven harmonic series of generators for that note. The former potentiometer used alone will give a range .of .odd harmonic tones, and the two potentiometers used together will give a range of complete series tones. If the latter potentiometer be used alone (giving the even harmonics) it will be .noted that this constitutes a completeseries of .tones but sounding anoctave higher in fundamental pitch.

With the above arrangement the :number Vof the vbus bars can be reduced to three `as shown in Figure 2 by joining together the two potentiometers and .thereby forming a single composite potentiometer centre tapped, the voltage applied to the two ends and the centreV tapping being controlled by the three bus bars. Thus, in this gure the potentiometer 5d has its tappings 6a connected `to the even harmonic control valves, and the potentiometer 5b has 'its tappings Bb connected to the odd harmonic control valves. Ihe two potentiometers are joined in series as shown, and, when the key is actuated the potentiometer 5a is connected between bus bar 3a and a common bus bar 4, and the potentiometer 5b isconnected between bus bar 3b and said 4common bus bar 4. The potential of 'the -bus bars (controlled by the stops) will determine whether the potentiometer 5b having the odd harmonic tappings, or whether both potentiometers 5a and 5b will be operative. The-arrangement is preferably such that the harmonic tappings of low order are towards the ends which are connected to the two outside bus vbars 3a, v3b while those of high order are towards the centre junction which is connected to the centre bus bar 4. With this arrangement a great range of tones may be obtained by means of three controls.

Sliders would preferably be employed to enable either equal or irregular spacing of the tapping points of th-e potentiometers to be provided.

Stops corresponding to sixteen, eight, four and two foot pitches may be represented by the requisite number of potentiometers.

A common potentiometer for the harmonics of each key, as above described, is usually satisfactory provided the resistance of said potentiometer is low compared to the circuits it energises. It is obvious, however, that instead of using one common potentiometer for a number of tapping points or sliders, a separate potentiometer for each tapping point or slider may be employed.

I claim:

1. An electrical musical instrument comprising a multiplicity of tone generator units each adapted to produce sound according to the degree of direct current polarisation applied thereto, bus bars, stops for controlling the direct current potentials of said bus bars, keys, potentiometer resistances corresponding to said keys, means whereby in response to actuation Yof a given one ofrsaid keys the corresponding potentiometer resistance is connected across said bus bars, and means coupling tapped points of said potentiometer resistance to generator unitsappertaining to said key, whereby, upon actuation of said key, direct current polarisation will be applied t0 said generator units to a degree. depending on the location of said tapped points Yand on the potentials given to said bus bars by said stops.

2. An electrical musical instrument comprising a multiplicity of tone generator units each adapted to produce sound according to the degree of direct current polarisation applied thereto, bus bars, stops for controlling the direct current potentials of said -bus bars, keys, potentiometer resistances corresponding to said keys, means Whereby'in response to actuation of a given one of said keys the corresponding potentiometer resistance is connected across said bus bars, and means permanently coupling tapped points of said potentiometer resistance to generator units appertaining to said key, whereby, upon actuation of said key, direct current polarisation will be applied to said generator units to a degree depending Aon the location of said tapped points and on the potentials given to said bus bars by said stops.

3. An electrical musical instrument comprising a multiplicity of tone generator units each adapted to produce sound according to the degree of direct current polarisation applied thereto, bus bars, stops for controlling the direct current potentials of said bus bars, keys, potentiometer resistances corresponding to said keys, means whereby in response to actuation oi a given one of said keys the corresponding potentiometer resistance is connected across said bus bars, and means coupling tapped points of said potentiometer resistance to generator units adapted to produce partials of the note appertaining to said key, whereby, upon actuation of said key, direct current polarisation will be applied to said generator units to a degree depending on the location of said tapped points and on the potential given to said bus bars by said stops.

4. An electrical musical instrument comprising a multiplicity of tone generator units each adapted to produce sound according to the degree of direct current polarisation applied thereto, bus bars, stops for controlling the direct current potentials of said bus bars, keys, potentiometer resistances corresponding to said keys, means whereby in response to actuation of a given one of said keys a potentiometer resistance corresponding to said key is connected across a pair of said bus bars, and another potentiometer resistance corresponding to said key is connected across a different pair of said bus bars, and means coupling tapped points of said potentiometer resistances to generator units adapted to produce partials of the note appertaining to said key, whereby, upon actuation of said key, direct current polarisation Will be applied to said generator units to a degree depending on the location of said tapped points and on the potential given to said bus bars by said stops. the tapped points of the potentiometer resistance which is connected across the rst pair of bus bars being coupledto generator units adapted to produce the odd partials, and the tapped points of the other potentiometer resistance being coupled to generator units adapted to produce the even partials.

5. An electrical musical instrument comprising a multiplicity of tone generator units each adapted to produce sound according to the degree LESLIE EDWIN ALEXANDER BOURN.

REFERENCES CITED The following references are o1' record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,233,948 Kock Mar. 4, 1941 2,237,105 Miessner Apr. 1, 1941 2,276,390 Hanert Mar. 17, 1942 2,403,090 Larsen July 2, 1946 FOREIGN PATENTS Number Country Date 501,520 Great Britain Feb. 28, 1239 

